Piezoelectric ceramic

ABSTRACT

The present invention has an object to provide piezoelectric ceramics containing no lead, having a high Curie point, and further, having excellent piezoelectric properties, particularly large Qmax. The piezoelectric ceramics contain, as a main component, a bismuth layer-structured compound having (M II   1-x Ln x )Bi 4 Ti 4 O 15  crystals (M II  is an element selected from Sr, Ba, and Ca, Ln is an element selected from lanthanoids, and x is within a range of 0&lt;x≦0.5) and further contain, as secondary components, at least one of Mn oxide and Co oxide, and lanthanoid, wherein the lanthanoid being the secondary component is contained within a range of 0.02 to 0.12 wt % in terms of oxide thereof.

TECHNICAL FIELD

The present invention relates to piezoelectric ceramics and, inparticular, relates to piezoelectric ceramics that can be used in fieldsof resonators, high temperature sensors, and so on by utilizingthickness longitudinal vibration of a bismuth layer-structured compound.

BACKGROUND ART

Piezoelectric ceramics have been widely used not only in a field ofelectronic devices such as resonators and filters, but also in productsand the like such as sensors and actuators that use electric charge anddisplacement.

The conventional piezoelectric ceramics are generally ferroelectricshaving a perovskite structure, such as lead titanate zirconate of thetetragonal system or trigonal system (PbZrO₃-PbTiO₃ solid solution,hereinafter referred to as PZT), or lead titanate of the tetragonalsystem (PbTiO₃, hereinafter referred to as PT). By adding secondarycomponents to these materials, there have been obtained ones havingvarious piezoelectric properties.

However, many of these PZT-based or PT-based piezoelectric ceramics haveCurie points of about 200 to 400° C. and thus become paraelectrics athigher temperatures to lose the piezoelectric properties thereof so thatthey can not be applied to usage at high temperatures, for example,nuclear reactor control sensors and the like. Further, the foregoingPZT-based or PT-based piezoceramics contain about 60 to 70 wt % leadoxide (PbO) and therefore are not preferable also in terms of ecologyand prevention of environmental pollution.

In order to meet such a demand, there is disclosed, as piezoelectricceramics having a high Curie point and containing no lead oxide at all,for example, a piezoelectric ceramic element using a piezoelectricceramic composition containing SrBi₄Ti₄O₁₅ as a main component andfurther containing at least one of Sc and Y in a range of 0.1 mol orless relative to 1 mol Bi in the main component (Unexamined PatentPublication No. 2001-172078).

Further, there are disclosed piezoelectric ceramics composed of abismuth layer-structured compound containing (Sr_(x)Ln_(1-x))Bi₄Ti₄O₁₅crystals (Unexamined Patent Publication No. 2000-143340), andpiezoelectric ceramics composed of a bismuth layer-structured compoundcontaining M^(II)Bi₄Ti₄O₁₅ crystals (M^(II) is an element selected fromSr, Ba, and Ca) (Unexamined Patent Publication No. 2001-192267).

Here, in case of a resonator, since it is used as an inductor, there arerequired piezoelectric ceramics in which Qm (mechanical quality factor),one of important properties in the piezoelectric properties, or Qmax(maximum value of Q=tan θ, θ:phase) between a resonant frequency and anantiresonant frequency, is large.

However, with respect to the piezoelectric ceramic element disclosed inUnexamined Patent Publication No. 2001-172078, there has been a problemthat although an electromechanical coupling coefficient kt and aresonant frequency temperature change rate frTC from −20° C. to 80° C.are improved, the foregoing Qmax is insufficient and therefore it doesnot have the sufficient piezoelectric properties applicable to theresonator.

On the other hand, the piezoelectric ceramics disclosed in UnexaminedPatent Publication No. 2000-143340 or Unexamined Patent Publication No.2001-192267 have large Qmax, but demands have been made for ones havinglarger Qmax as piezoelectric ceramics using thickness longitudinalvibration.

DISCLOSURE OF THE INVENTION

Therefore, the present invention has been made in view of the foregoingcircumstances and provides piezoelectric ceramics containing no lead,having a high Curie point, and further, having excellent piezoelectricproperties, particularly large Qmax.

For accomplishing such an object, the present invention is configured tocontain, as a main component, a bismuth layer-structured compound having(M^(II) _(1-x)Ln_(x))Bi₄Ti₄O₁₅ crystals (M^(II) is an element selectedfrom Sr, Ba, and Ca, Ln is an element selected from lanthanoids, and xis within a range of 0<x≧0.5) and further contain, as secondarycomponents, at least one of Mn oxide and Co oxide, and lanthanoid,wherein the content of the lanthanoid being the secondary componentfalls within a range of 0.02 to 0.12 wt % in terms of oxide thereof.

As a preferred mode of the present invention, it is configured such thatthe content of said Mn oxide or Co oxide falls within a range of 0.02 to0.62 wt % in terms of MnO or CoO.

As a preferred mode of the present invention, it is configured such thatlanthanoid selected as Ln is any one of La, Pr, Sm, Gd, Dy, and Ho.

As a preferred mode of the present invention, it is configured such thatthe lanthanoid being the secondary component is any one of Pr, Nd, Sm,Gd, Dy, and Ho.

According to the present invention as described above, there are enabledpiezoelectric ceramics excellent in piezoelectric properties such thatno lead is contained, a Curie point is high, i.e. 450° C. or more, andfurther, by suitably selecting M^(II), Qmax becomes 12 or more at 16 MHzbeing a lower limit of harmonic vibration (third order vibration)utilizing thickness longitudinal vibration, or large Qmax of 6 or moreis achieved at 60 MHz being an upper limit of the harmonic vibration(third order vibration). The achievement of large Qmax enables reductionin size of a resonator, a high temperature sensor, and the like.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, an embodiment of the present invention will be described.

Piezoelectric ceramics of the present invention are piezoelectricceramics that contain as a main component a bismuth layer-structuredcompound having (M^(II) _(1-x)Ln_(x))Bi₄Ti₄O₁₅ crystals and furthercontain, as secondary components, lanthanoid and at least one of Mnoxide and Co oxide, and are used in thickness longitudinal vibration.

The foregoing M^(II) is an element selected from Sr, Ba, and Ca, Ln isan element selected from lanthanoids, and x is set within a range of0<x≧0.5, preferably 0.01≧x≧0.2.

M^(II) can be suitably selected depending on a vibration range, to beused, of the piezoelectric ceramics, for example, the lower limit side(16 to 33 MHz) or the upper limit side (33 to 60 MHz) of the harmonicvibration (third order vibration).

Lanthanoid selected as Ln is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho,Er, Tm, Yb, or Lu. Among them, particularly La, Pr, Sm, Gd, Dy, or Ho ispreferable. It is considered that such Ln substitutes M^(II) sites ofM^(II)Bi₄Ti₄O₁₅ crystals. If Ln does not substitute the M^(II) sites inthe foregoing range (when x=0), there is obtained no effect to improveQmax (maximum value of Q=tan θ, θ:phase) between a resonant frequencyand an antiresonant frequency. On the other hand, if the content of Lnsubstituting the M^(II) sites exceeds 50 mol % (when x>0.5), Qmaxbecomes low, which is not preferable.

Lanthanoid contained as the secondary component is contained in thepiezoelectric ceramics within a range of 0.02 to 0.12 wt %, preferably0.05 to 0.1 wt % in terms of oxide thereof. It is considered that suchlanthanoid as the secondary component exists at grain boundaries of the(M^(II) _(1-x)Ln_(x))Bi₄Ti₄O₁₅ crystals. If the content of thislanthanoid is less than 0.02 wt %, Qmax becomes low and the densitybecomes insufficient, which is not preferable. On the other hand, if thecontent exceeds 0.12 wt %, there is obtained no effect to improve Qmax.Lanthanoid as the secondary component is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd,Tb, Dy, Ho, Er, Tm, Yb, or Lu. Among them, particularly Pr, Nd, Sm, Gd,Dy, or Ho is preferable.

The content of at least one of Mn oxide and Co oxide contained as thesecondary component falls within a range of 0.02 to 0.62 wt %,preferably 0.03 to 0.43 wt % in terms of MnO or CoO. If the content ofone of Mn oxide and Co oxide or the total content of the two is lessthan 0.02 wt %, there is obtained no effect to improve Qmax, while, ifit exceeds 0.62 wt %, polarization becomes difficult, which is notpreferable.

Incidentally, the piezoelectric ceramics of the present invention maycontain Mn, Ba, Ca, Zr, Sn, Mo, W, Y, Zn, Sb, Si, Nb, Ta, or the like asan impurity or a minor additive. In this event, the content thereof ispreferably 0.01 wt % or less of the whole in terms of oxide thereof.

With respect to the (M^(II) _(1-x)Ln_(x))Bi₄Ti₄O₁₅ crystals being themain component of the piezoelectric ceramics of the present invention,for example, the ratio of M^(II), Ln, or Bi relative to Ti may tolerablydeviate from a stoichiometric composition in a range of about ±5% orless.

A crystal grain of the piezoelectric ceramics of the present inventionis spindle-shaped or needle-shaped, and its average grain size is notparticularly limited and is, for example, 1 to 10 μm, preferably about 3to 5 μm in a major axis direction thereof.

The piezoelectric ceramics of the present invention as described abovehave a high Curie point of 450° C. or more and are further such that, bysuitably selecting M^(II), Qmax becomes 12 or more at 16 MHz being alower limit of harmonic vibration (third order vibration) utilizingthickness longitudinal vibration, or large Qmax of 6 or more is achievedat 60 MHz being an upper limit of the harmonic vibration (third ordervibration). Therefore, they are applicable to a resonator, a hightemperature sensor, and the like. Further, since no lead is contained,they are safe enough also in terms of preservation of the environment.Moreover, size reduction in the resonator, the high temperature sensor,and the like is enabled.

Next, description will be given about one example of production of thepiezoelectric ceramics of the present invention.

First, substances to become a main component [(M^(II)_(1-x)Ln_(x))Bi₄Ti₄O₁₅] and at least one of Mn oxide and Co oxide beinga secondary component are weighed as starting substances and wet mixedby the use of a ball mill or the like. Specifically, powder rawmaterials of compounds that can be changed to oxides by sintering, forexample, carbonate, hydroxide, oxalate, nitrate, and the like,concretely M^(II)CO₃ (M^(II) is an element selected from Sr, Ba, andCa), Ln₂O₃ (Ln is lanthanoid), Bi₂O₃, TiO₂, MnO, CoO, MnCO₃, and thelike, are weighed so that the main component [M^(II)_(1-x)Ln_(x))Bi₄Ti₄O₁₅] has a desired composition, and are wet mixed bythe use of the ball mill or the like.

This mixture is dried and is then subjected to calcination at 700 to1000° C., preferably about 750 to 850° C. for about 1 to 3 hours. Theobtained calcined thing is added with lanthanoid as a secondarycomponent, for example, a compound composed of Ln₂O₃ (Ln is lanthanoid),and formed into a slurry which is then wet milled by the use of the ballmill or the like. Subsequently, the calcined thing is dried and is thengranulated by adding a binder such as polyvinyl alcohol (PVA) dependingon necessity. Thereafter, this granulated powder is subjected to pressmolding (pressure 100 to 400 MPa) to obtain a compact. As describedabove, since lanthanoid as the secondary component is added after thecalcination, it is considered that lanthanoid as the secondary componentexists at grain boundaries of the (M^(II) _(1-x)Ln_(x))Bi₄Ti₄O₁₅crystals.

Then, the foregoing compact is subjected to sintering at about 1100 to1250° C. for 1 to 5 hours, and a polarization process (a polarizationelectric field is 1.1 times or more a coercive electric field) isapplied to this sintered compact in a silicon oil bath at 150 to 250° C.to obtain piezoelectric ceramics. The sintering may be carried out inthe atmosphere. Alternatively, it may be carried out in an atmospherewith an oxygen partial pressure lower or higher the atmosphere, or in apure oxygen atmosphere. When the binder such as PVA is used, it ispreferable to perform a heat treatment before the sintering to therebyvolatilize the binder.

Next, the present invention will be described in further detail byexamples, but the present invention is not limited by these examples inany aspect.

EXAMPLE 1

Respective powder raw materials of SrCO₃, La₂O₃, Bi₂O₃, TiO₂, MnCO₃, andPr₂O₃ were prepared as starting substances and weighed so that a finalcomposition of a main component should be (Sr_(0.95)La_(0.05))Bi₄Ti₄O₁₅and the content of MnCO₃ being a secondary component should be 0.3 wt %in terms of MnO, and were then subjected to ball mill mixing (about 16hours) in pure water by the use of zirconia balls.

The obtained mixture was fully dried, and was then subjected totemporary molding and further subjected to calcination in the air for 2hours. The calcination temperature was selected from a range of 800 to1000° C. Thereafter, Pr₂O₃ was weighed and added to the obtainedcalcined things so that the contents thereof should be as shown in Table1 below. Then, wet milling and mixing of the additive (Pr₂O₃) werecarried out by the use of the foregoing ball mill. Subsequently, afterdrying, 6 wt % pure water was added as a binder and press molding wasperformed, thereby obtaining six kinds of temporary compacts each havinga length of 40 mm, a width of 40 mm, and a thickness of about 13 mm.These temporary compacts were subjected to vacuum packing and thensubjected to isostatic molding under a pressure of 245 MPa.

Then, the foregoing compacts were subjected to sintering (in theatmosphere) at about 1120 to 1235° C. for 4 hours to thereby obtainsintered compacts. Subsequently, a plate-like member having a length of30 mm, a width of 30 mm, and a thickness of 0.55 mm was cut out fromeach of the sintered compacts and was subjected to lap polishing tothereby obtain a thin plate having a thickness of 435 μm. Thereafter, Cuelectrodes were formed on both surfaces of each thin plate by vacuumdeposition.

Then, a polarization process was carried out such that an electric fieldof 1.5×Ec (MV/m) or more was applied in a silicon oil bath at 250° C.for 1 minute so as to have a thickness direction of each thin platecoincide with a polarization direction. Herein, Ec represents a coerciveelectric field of each sintered compact at 250° C.

Each of the sintered compacts thus polarized was subjected to etching toremove the Cu electrodes by the use of a ferric chloride solution andwas then cut into a size of 7 mm long and 4.5 mm wide, thereby obtainingpiezoelectric ceramics (Sample 1-1 to Sample 1-6). On both surfaces ofeach of the piezoelectric ceramics, Ag electrodes (diameter 1.5 mm,thickness 1 μm) for evaluating thickness longitudinal vibration wereformed by the vacuum deposition method.

With respect to each of the piezoelectric ceramics thus produced, Qmaxwas measured under the following condition and a result thereof wasshown in Table 1 below.

Measurement Condition of Qmax

By the use of an impedance analyzer HP4194A produced by Hewlett-PackardDevelopment Company, L.P., the impedance characteristic was measured ina three-order harmonic mode of thickness longitudinal vibration (16 MHz)to derive Qmax. Qmax contributes to low-voltage oscillation as aresonator and Qmax at 16 MHz is required to be 12 or more. TABLE 1Piezoelectric Pr Content Ceramics (wt %) Qmax (16 MHz) *Sample 1-1 011.6 Sample 1-2 0.02 12.3 Sample 1-3 0.05 12.6 Sample 1-4 0.10 12.5Sample 1-5 0.12 12.0 *Sample 1-6 0.14 10.3Sample with * mark deviates from the present invention.

As shown in Table 1, it was confirmed that the piezoelectric ceramics(Sample 1-2 to Sample 1-5) containing (Sr_(0.95)La_(0.05))Bi₄Ti₄O₁₅being the main component, and Mn oxide and Pr oxide as the secondarycomponents, and further, containing the Pr oxide in a range of 0.02 to0.12 wt % in terms of Pr₂O₃, all had Qmax of 12 or more. Further, Curiepoints of these piezoelectric ceramics (measured by the use of LCR meterHP4394A produced by Hewlett-Packard Development Company, L.P. and anelectric furnace) were all 530° C. or higher.

EXAMPLE 2

First, respective powder raw materials of SrCO₃, La₂O₃, Bi₂O₃, TiO₂,MnCO₃, and Pr₂O₃ were prepared as starting substances and weighed sothat a final composition of a main component should be(Sr_(0.9)La_(0.1))Bi₄Ti₄O₁₅ and the content of MnCO₃ being a secondarycomponent should be 0.24 wt % in terms of MnO, and were then subjectedto ball mill mixing (about 16 hours) in pure water by the use ofzirconia balls.

Thereafter, the obtained mixture was used to obtain piezoelectricceramics (Sample 2-1 to Sample 2-6) like in Example 1. However, Pr₂O₃was weighed and added to calcined things so that the contents thereofshould be as shown in Table 2 below. On both surfaces of each of thepiezoelectric ceramics, Ag electrodes (diameter 1.5 mm, thickness 1 μm)for evaluating thickness longitudinal vibration were formed by thevacuum deposition method.

With respect to each of the piezoelectric ceramics thus produced, Qmaxwas measured under the same condition as in Example 1, and a resultthereof was shown in Table 2 below. TABLE 2 Piezoelectric Pr ContentCeramics (wt %) Qmax (16 MHz) *Sample 2-1 0 11.8 Sample 2-2 0.02 13.0Sample 2-3 0.05 13.4 Sample 2-4 0.10 12.9 Sample 2-5 0.12 12.0 *Sample2-6 0.14 7.2Sample with * mark deviates from the present invention.

As shown in Table 2, it was confirmed that the piezoelectric ceramics(Sample 2-2 to Sample 2-5) containing (Sr_(0.9)La_(0.1))Bi₄Ti₄O₁₅ beingthe main component, and Mn oxide and Pr oxide as the secondarycomponents, and further, containing the Pr oxide in a range of 0.02 to0.12 wt % in terms of Pr₂O₃, all had Qmax of 12 or more. Further, Curiepoints of these piezoelectric ceramics were measured like in Example 1and consequently were all 510° C. or higher.

EXAMPLE 3

First, respective powder raw materials of SrCO₃, La₂O₃, Bi₂O₃, TiO₂,MnCO₃, and Sm₂O₃ were prepared as starting substances and weighed sothat a final composition of a main component should be(Sr_(0.9)La_(0.1))Bi₄Ti₄O₁₅ and the content of MnCO₃ being a secondarycomponent should be 0.3 wt % in terms of MnO, and were then subjected toball mill mixing (about 16 hours) in pure water by the use of zirconiaballs.

Thereafter, the obtained mixture was used to obtain piezoelectricceramics (Sample 3-1 to Sample 3-6) like in Example 1. However, Sm₂O₃was weighed and added to calcined things so that the contents thereofshould be as shown in Table 3 below. On both surfaces of each of thepiezoelectric ceramics, Ag electrodes (diameter 1.5 mm, thickness 1 μm)for evaluating thickness longitudinal vibration were formed by thevacuum deposition method.

With respect to each of the piezoelectric ceramics thus produced, Qmaxwas measured under the same condition as in Example 1, and a resultthereof was shown in Table 3 below. TABLE 3 Piezoelectric Sm ContentCeramics (wt %) Qmax (16 MHz) *Sample 3-1 0 11.8 Sample 3-2 0.02 12.2Sample 3-3 0.05 12.3 Sample 3-4 0.10 12.2 Sample 3-5 0.12 12.0 *Sample3-6 0.14 10.6Sample with * mark deviates from the present invention.

As shown in Table 3, it was confirmed that the piezoelectric ceramics(Sample 3-2 to Sample 3-5) containing (Sr_(0.9)La_(0.1))Bi₄Ti₄O₁₅ beingthe main component, and Mn oxide and Sm oxide as the secondarycomponents, and further, containing the Sm oxide in a range of 0.02 to0.12 wt % in terms of Sm₂O₃, all had Qmax of 12 or more. Further, Curiepoints of these piezoelectric ceramics were measured like in Example 1and consequently were all 510° C. or higher.

EXAMPLE 4

First, respective powder raw materials of SrCO₃, La₂O₃, Bi₂O₃, TiO₂,MnCO₃, and Nd₂O₃ were prepared as starting substances and weighed sothat a final composition of a main component should be(Sr_(0.8)La_(0.2))Bi₄Ti₄O₁₅ and the content of MnCO₃ being a secondarycomponent should be 0.18 wt % in terms of MnO, and were then subjectedto ball mill mixing (about 16 hours) in pure water by the use ofzirconia balls.

Thereafter, the obtained mixture was used to obtain piezoelectricceramics (Sample 4-1 to Sample 4-6) like in Example 1. However, Nd₂O₃was weighed and added to calcined things so that the contents thereofshould be as shown in Table 4 below. On both surfaces of each of thepiezoelectric ceramics, Ag electrodes (diameter 1.5 mm, thickness 1 μm)for evaluating thickness longitudinal vibration were formed by thevacuum deposition method.

With respect to each of the piezoelectric ceramics thus produced, Qmaxwas measured under the same condition as in Example 1, and a resultthereof was shown in Table 4 below. TABLE 4 Piezoelectric Nd ContentCeramics (wt %) Qmax (16 MHz) *Sample 4-1 0 11.6 Sample 4-2 0.02 12.5Sample 4-3 0.05 12.9 Sample 4-4 0.10 12.6 Sample 4-5 0.12 12.3 *Sample4-6 0.14 8.3Sample with * mark deviates from the present invention.

As shown in Table 4, it was confirmed that the piezoelectric ceramics(Sample 4-2 to Sample 4-5) containing (Sr_(0.8)La_(0.2))Bi₄Ti₄O₁₅ beingthe main component, and Mn oxide and Nd oxide as the secondarycomponents, and further, containing the Nd oxide in a range of 0.02 to0.12 wt % in terms of Nd₂O₃, all had Qmax of 12 or more. Further, Curiepoints of these piezoelectric ceramics were measured like in Example 1and consequently were all 490° C. or higher.

EXAMPLE 5

First, respective powder raw materials of SrCO₃, La₂O₃, Bi₂O₃, TiO₂,MnCO₃, and Gd₂O₃ were prepared as starting substances and weighed sothat a final composition of a main component should be(Sr_(0.7)La_(0.3))Bi₄Ti₄O₁₅ and the content of MnCO₃ being a secondarycomponent should be 0.24 wt % in terms of MnO, and were then subjectedto ball mill mixing (about 16 hours) in pure water by the use ofzirconia balls.

Thereafter, the obtained mixture was used to obtain piezoelectricceramics (Sample 5-1 to Sample 5-6) like in Example 1. However, Gd₂O₃was weighed and added to calcined things so that the contents thereofshould be as shown in Table 5 below. On both surfaces of each of thepiezoelectric ceramics, Ag electrodes (diameter 1.5 mm, thickness 1 μm)for evaluating thickness longitudinal vibration were formed by thevacuum deposition method.

With respect to each of the piezoelectric ceramics thus produced, Qmaxwas measured under the same condition as in Example 1, and a resultthereof was shown in Table 5 below. TABLE 5 Piezoelectric Gd ContentCeramics (wt %) Qmax (16 MHz) *Sample 5-1 0 11.4 Sample 5-2 0.02 12.1Sample 5-3 0.05 12.2 Sample 5-4 0.10 12.5 Sample 5-5 0.12 12.4 *Sample5-6 0.14 11.7Sample with * mark deviates from the present invention.

As shown in Table 5, it was confirmed that the piezoelectric ceramics(Sample 5-2 to Sample 5-5) containing (Sr_(0.7)La_(0.3))Bi₄Ti₄O₁₅ beingthe main component, and Mn oxide and Gd oxide as the secondarycomponents, and further, containing the Gd oxide in a range of 0.02 to0.12 wt % in terms of Gd₂O₃, all had Qmax of 12 or more. Further, Curiepoints of these piezoelectric ceramics were measured like in Example 1and consequently were all 460° C. or higher.

EXAMPLE 6

First, respective powder raw materials of SrCO₃, La₂O₃, Bi₂O₃, TiO₂,MnCO₃, and Ho₂O₃ were prepared as starting substances and weighed sothat a final composition of a main component should be(Sr_(0.6)La_(0.4))Bi₄Ti₄O₁₅ and the content of MnCO₃ being a secondarycomponent should be 0.24 wt % in terms of MnO, and were then subjectedto ball mill mixing (about 16 hours) in pure water by the use ofzirconia balls.

Thereafter, the obtained mixture was used to obtain piezoelectricceramics (Sample 6-1 to Sample 6-6) like in Example 1. However, Ho₂O₃was weighed and added to calcined things so that the contents thereofshould be as shown in Table 6 below. On both surfaces of each of thepiezoelectric ceramics, Ag electrodes (diameter 1.5 mm, thickness 1 μm)for evaluating thickness longitudinal vibration were formed by thevacuum deposition method.

With respect to each of the piezoelectric ceramics thus produced, Qmaxwas measured under the same condition as in Example 1, and a resultthereof was shown in Table 6 below. TABLE 6 Piezoelectric Ho ContentCeramics (wt %) Qmax (16 MHz) *Sample 6-1 0 11.2 Sample 6-2 0.02 12.2Sample 6-3 0.05 12.6 Sample 6-4 0.10 12.5 Sample 6-5 0.12 12.0 *Sample6-6 0.14 9.5Sample with * mark deviates from the present invention.

As shown in Table 6, it was confirmed that the piezoelectric ceramics(Sample 6-2 to Sample 6-5) containing (Sr_(0.6)La_(0.4))Bi₄Ti₄O₁₅ beingthe main component, and Mn oxide and Ho oxide as the secondarycomponents, and further, containing the Ho oxide in a range of 0.02 to0.12 wt % in terms of Ho₂O₃, all had Qmax of 12 or more. Further, Curiepoints of these piezoelectric ceramics were measured like in Example 1and consequently were all 450° C. or higher.

EXAMPLE 7

First, respective powder raw materials of SrCO₃, La₂O₃, Bi₂O₃, TiO₂,MnCO₃, and Dy₂O₃ were prepared as starting substances and weighed sothat a final composition of a main component should be(Sr_(0.8)La_(0.2))Bi₄Ti₄O₁₅ and the content of MnCO₃ being a secondarycomponent should be 0.12 wt % in terms of MnO, and were then subjectedto ball mill mixing (about 16 hours) in pure water by the use ofzirconia balls.

Thereafter, the obtained mixture was used to obtain piezoelectricceramics (Sample 7-1 to Sample 7-6) like in Example 1. However, Dy₂O₃was weighed and added to calcined things so that the contents thereofshould be as shown in Table 7 below. On both surfaces of each of thepiezoelectric ceramics, Ag electrodes (diameter 1.5 mm, thickness 1 μm)for evaluating thickness longitudinal vibration were formed by thevacuum deposition method.

With respect to each of the piezoelectric ceramics thus produced, Qmaxwas measured under the same condition as in Example 1, and a resultthereof was shown in Table 7 below. TABLE 7 Piezoelectric Dy ContentCeramics (wt %) Qmax (16 MHz) *Sample 7-1 0 11.6 Sample 7-2 0.02 12.6Sample 7-3 0.05 13.0 Sample 7-4 0.10 12.9 Sample 7-5 0.12 12.3 *Sample7-6 0.14 9.5Sample with * mark deviates from the present invention.

As shown in Table 7, it was confirmed that the piezoelectric ceramics(Sample 7-2 to Sample 7-5) containing (Sr_(0.8)La_(0.2))Bi₄Ti₄O₁₅ beingthe main component, and Mn oxide and Dy oxide as the secondarycomponents, and further, containing the Dy oxide in a range of 0.02 to0.12 wt % in terms of Dy₂O₃, all had Qmax of 12 or more. Further, Curiepoints of these piezoelectric ceramics were measured like in Example 1and consequently were all 490° C. or higher.

EXAMPLE 8

First, respective powder raw materials of SrCO₃, La₂O₃, Bi₂O₃, TiO₂,MnCO₃, and Er₂O₃ were prepared as starting substances and weighed sothat a final composition of a main component should be(Sr_(0.9)La_(0.1))Bi₄Ti₄O₁₅ and the content of MnCO₃ being a secondarycomponent should be 0.06 wt % in terms of MnO, and were then subjectedto ball mill mixing (about 16 hours) in pure water by the use ofzirconia balls.

Thereafter, the obtained mixture was used to obtain piezoelectricceramics (Sample 8-1 to Sample 8-6) like in Example 1. However, Er₂O₃was weighed and added to calcined things so that the contents thereofshould be as shown in Table 8 below. On both surfaces of each of thepiezoelectric ceramics, Ag electrodes (diameter 1.5 mm, thickness 1 μm)for evaluating thickness longitudinal vibration were formed by thevacuum deposition method.

With respect to each of the piezoelectric ceramics thus produced, Qmaxwas measured under the same condition as in Example 1, and a resultthereof was shown in Table 8 below. TABLE 8 Piezoelectric Er ContentCeramics (wt %) Qmax (16 MHz) *Sample 8-1 0 11.8 Sample 8-2 0.02 12.2Sample 8-3 0.05 12.3 Sample 8-4 0.10 12.1 Sample 8-5 0.12 12.0 *Sample8-6 0.14 10.0Sample with * mark deviates from the present invention.

As shown in Table 8, it was confirmed that the piezoelectric ceramics(Sample 8-2 to Sample 8-5) containing (Sr_(0.9)La_(0.1))Bi₄Ti₄O₁₅ beingthe main component, and Mn oxide and Er oxide as the secondarycomponents, and further, containing the Er oxide in a range of 0.02 to0.12 wt % in terms of Er₂O₃, all had Qmax of 12 or more. Further, Curiepoints of these piezoelectric ceramics were measured like in Example 1and consequently were all 510° C. or higher.

EXAMPLE 9

First, respective powder raw materials of SrCO₃, BaCO₃, La₂O₃, Bi₂O₃,TiO₂, MnCO₃, and Pr₂O₃ were prepared as starting substances and weighedso that a final composition of a main component should be(Sr_(0.8)Ba_(0.1)La_(0.1))Bi₄Ti₄O₁₅ and the content of MnCO₃ being asecondary component should be 0.3 wt % in terms of MnO, and were thensubjected to ball mill mixing (about 16 hours) in pure water by the useof zirconia balls.

Thereafter, the obtained mixture was used to obtain piezoelectricceramics (Sample 9-1 to Sample 9-6) like in Example 1. However, Pr₂O₃was weighed and added to calcined things so that the contents thereofshould be as shown in Table 9 below. On both surfaces of each of thepiezoelectric ceramics, Ag electrodes (diameter 1.5 mm, thickness 1 μm)for evaluating thickness longitudinal vibration were formed by thevacuum deposition method.

With respect to each of the piezoelectric ceramics thus produced, Qmaxwas measured under the same condition as in Example 1, and a resultthereof was shown in Table 9 below. TABLE 9 Piezoelectric Pr ContentCeramics (wt %) Qmax (16 MHz) *Sample 9-1 0 10.6 Sample 9-2 0.02 12.1Sample 9-3 0.05 12.3 Sample 9-4 0.10 12.2 Sample 9-5 0.12 12.0 *Sample9-6 0.14 10.4Sample with * mark deviates from the present invention.

As shown in Table 9, it was confirmed that the piezoelectric ceramics(Sample 9-2 to Sample 9-5) containing(Sr_(0.8)Ba_(0.1)La_(0.1))Bi₄Ti₄O₁₅ being the main component, and Mnoxide and Pr oxide as the secondary components, and further, containingthe Pr oxide in a range of 0.02 to 0.12 wt % in terms of Pr₂O₃, all hadQmax of 12 or more. Further, Curie points of these piezoelectricceramics were measured like in Example 1 and consequently were all 490°C. or higher.

EXAMPLE 10

First, respective powder raw materials of SrCO₃, Sm₂O₃, Bi₂O₃, TiO₂,MnCO₃, and Gd₂O₃ were prepared as starting substances and weighed sothat a final composition of a main component should be(Sr_(0.95)Sm_(0.05))Bi₄Ti₄O₁₅ and the content of MnCO₃ being a secondarycomponent should be 0.24 wt % in terms of MnO, and were then subjectedto ball mill mixing (about 16 hours) in pure water by the use ofzirconia balls.

Thereafter, the obtained mixture was used to obtain piezoelectricceramics (Sample 10-1 to Sample 10-6) like in Example 1. However, Gd₂O₃was weighed and added to calcined things so that the contents thereofshould be as shown in Table 10 below. On both surfaces of each of thepiezoelectric ceramics, Ag electrodes (diameter 1.5 mm, thickness 1 μm)for evaluating thickness longitudinal vibration were formed by thevacuum deposition method.

With respect to each of the piezoelectric ceramics thus produced, Qmaxwas measured under the same condition as in Example 1, and a resultthereof was shown in Table 10 below. TABLE 10 Piezoelectric Gd ContentCeramics (wt %) Qmax (16 MHz) *Sample 10-1 0 11.8 Sample 10-2 0.02 13.1Sample 10-3 0.05 13.3 Sample 10-4 0.10 13.6 Sample 10-5 0.12 13.5*Sample 10-6 0.14 11.9Sample with * mark deviates from the present invention.

As shown in Table 10, it was confirmed that the piezoelectric ceramics(Sample 10-2 to Sample 10-5) containing (Sr_(0.95)Sm_(0.05))Bi₄Ti₄O₁₅being the main component, and Mn oxide and Gd oxide as the secondarycomponents, and further, containing the Gd oxide in a range of 0.02 to0.12 wt % in terms of Gd₂O₃, all had Qmax of 12 or more. Further, Curiepoints of these piezoelectric ceramics were measured like in Example 1and consequently were all 460° C. or higher.

EXAMPLE 11

First, respective powder raw materials of SrCO₃, La₂O₃, Bi₂O₃, TiO₂,MnCO₃, and Ho₂O₃ were prepared as starting substances and weighed sothat a final composition of a main component should be(Sr_(0.6)La_(0.4))Bi₄Ti₄O₁₅ and the content of MnCO₃ being a secondarycomponent should be 0.62 wt % in terms of MnO, and were then subjectedto ball mill mixing (about 16 hours) in pure water by the use ofzirconia balls.

Thereafter, the obtained mixture was used to obtain piezoelectricceramics (Sample 11-1 to Sample 11-6) like in Example 1. However, Ho₂O₃was weighed and added to calcined things so that the contents thereofshould be as shown in Table 11 below. On both surfaces of each of thepiezoelectric ceramics, Ag electrodes (diameter 1.5 mm, thickness 1 μm)for evaluating thickness longitudinal vibration were formed by thevacuum deposition method.

With respect to each of the piezoelectric ceramics thus produced, Qmaxwas measured under the same condition as in Example 1, and a resultthereof was shown in Table 11 below. TABLE 11 Piezoelectric Ho ContentCeramics (wt %) Qmax (16 MHz) *Sample 11-1 0 11.8 Sample 11-2 0.02 13.1Sample 11-3 0.05 13.5 Sample 11-4 0.10 13.4 Sample 11-5 0.12 12.8*Sample 11-6 0.14 10.2Sample with * mark deviates from the present invention.

As shown in Table 11, it was confirmed that the piezoelectric ceramics(Sample 11-2 to Sample 11-5) containing (Sr_(0.6)La_(0.4))Bi₄Ti₄O₁₅being the main component, and Mn oxide and Ho oxide as the secondarycomponents, and further, containing the Ho oxide in a range of 0.02 to0.12 wt % in terms of Ho₂O₃, all had Qmax of 12 or more. Further, Curiepoints of these piezoelectric ceramics were measured like in Example 1and consequently were all 450° C or higher.

EXAMPLE 12

First, respective powder raw materials of SrCO₃, Sm₂O₃, Bi₂O₃, TiO₂,CoO, and Er₂O₃ were prepared as starting substances and weighed so thata final composition of a main component should be(Sr_(0.9)Sm_(0.1))Bi₄Ti₄O₁₅ and the content of CoO being a secondarycomponent should be 0.3 wt %, and were then subjected to ball millmixing (about 16 hours) in pure water by the use of zirconia balls.

Thereafter, the obtained mixture was used to obtain piezoelectricceramics (Sample 12-1 to Sample 12-6) like in Example 1. However, Er₂O₃was weighed and added to calcined things so that the contents thereofshould be as shown in Table 12 below. On both surfaces of each of thepiezoelectric ceramics, Ag electrodes (diameter 1.5 mm, thickness 1 μm)for evaluating thickness longitudinal vibration were formed by thevacuum deposition method.

With respect to each of the piezoelectric ceramics thus produced, Qmaxwas measured under the same condition as in Example 1, and a resultthereof was shown in Table 12 below. TABLE 12 Piezoelectric Er ContentCeramics (wt %) Qmax (16 MHz) *Sample 12-1 0 10.3 Sample 12-2 0.02 12.0Sample 12-3 0.05 12.1 Sample 12-4 0.10 12.1 Sample 12-5 0.12 12.0*Sample 12-6 0.14 9.5Sample with * mark deviates from the present invention.

As shown in Table 12, it was confirmed that the piezoelectric ceramics(Sample 12-2 to Sample 12-5) containing (Sr_(0.9)Sm_(0.1))Bi₄Ti₄O₁₅being the main component, and Co oxide and Er oxide as the secondarycomponents, and further, containing the Er oxide in a range of 0.02 to0.12 wt % in terms of Er₂O₃, all had Qmax of 12 or more. Further, Curiepoints of these piezoelectric ceramics were measured like in Example 1and consequently were all 460° C. or higher.

COMPARATIVE EXAMPLE1

First, respective powder raw materials of SrCO₃, Bi₂O₃, TiO₂, Sc₂O₃, andMnCO₃ were prepared as starting substances and weighed so that a finalcomposition of a main component should be (Sr_(0.9)Sc_(0.1))Bi₄Ti₄O₁₅and the content of MnCO₃ being a secondary component should be 0.3 wt %in terms of MnO, and were then subjected to ball mill mixing (about 16hours) in pure water by the use of zirconia balls.

Thereafter, the obtained mixture was used to obtain piezoelectricceramics (Comparative Sample 1) like in Example 1. On both surfaces ofthis piezoelectric ceramics, Ag electrodes (diameter 1.5 mm, thickness 1μm) for evaluating thickness longitudinal vibration were formed by thevacuum deposition method.

With respect to the piezoelectric ceramics thus produced, Qmax wasmeasured under the same condition as in Example 1. As a result, Qmax was10.5 and did not satisfy the required characteristic of the resonator at16 MHz.

COMPARATIVE EXAMPLE 2

First, respective powder raw materials of SrCO₃, Bi₂O₃, TiO₂, Y₂O₃, andMnCO₃ were prepared as starting substances and weighed so that a finalcomposition of a main component should be (Sr_(0.9)Y_(0.1))Bi₄Ti₄O₁₅ andthe content of MnCO₃ being a secondary component should be 0.3 wt % interms of MnO, and were then subjected to ball mill mixing (about 16hours) in pure water by the use of zirconia balls.

Thereafter, the obtained mixture was used to obtain piezoelectricceramics (Comparative Sample 2) like in Example 1. On both surfaces ofthis piezoelectric ceramics, Ag electrodes (diameter 1.5 mm, thickness 1μm) for evaluating thickness longitudinal vibration were formed by thevacuum deposition method.

With respect to the piezoelectric ceramics thus produced, Qmax wasmeasured under the same condition as in Example 1. As a result, Qmax was11.5 and did not satisfy the required characteristic of the resonator at16 MHz.

COMPARATIVE EXAMPLE 3

First, respective powder raw materials of SrCO₃, Bi₂O₃, TiO₂, La₂O₃, andMnCO₃ were prepared as starting substances and weighed so that a finalcomposition of a main component should be (Sr_(0.9)La_(0.1))Bi₄Ti₄O₁₅and the content of MnCO₃ being a secondary component should be 0.18 wt %in terms of MnO, and were then subjected to ball mill mixing (about 16hours) in pure water by the use of zirconia balls.

Thereafter, the obtained mixture was used to obtain piezoelectricceramics (Comparative Sample 3) like in Example 1. On both surfaces ofthis piezoelectric ceramics, Ag electrodes (diameter 1.5 mm, thickness 1μm) for evaluating thickness longitudinal vibration were formed by thevacuum deposition method.

With respect to the piezoelectric ceramics thus produced, Qmax wasmeasured under the same condition as in Example 1. As a result, Qmax was11.8 and did not satisfy the required characteristic of the resonator at16 MHz.

EXAMPLE 13

First, respective powder raw materials of CaCO₃, La₂O₃, Bi₂O₃, TiO₂,MnCO₃, and Pr₂O₃ were prepared as starting substances and weighed sothat a final composition of a main component should be(Ca_(0.97)La_(0.03))Bi₄Ti₄O₁₅ and the content of MnCO₃ being a secondarycomponent should be 0.3 wt % in terms of MnO, and were then subjected toball mill mixing (about 16 hours) in pure water by the use of zirconiaballs.

Thereafter, like in Example 1, the obtained mixture was used to obtainpiezoelectric ceramics (Sample 13-1 to Sample 13-6) each having a lengthof 2 mm, a width of 1.25 mm, and a thickness of 435 μm. However, Pr₂O₃was weighed and added to calcined things so that the contents thereofshould be as shown in Table 13 below. On both surfaces of each of thepiezoelectric ceramics, Ag electrodes (diameter 1.5 mm, thickness 1 μm)for evaluating thickness longitudinal vibration were formed by thevacuum deposition method.

With respect to each of the piezoelectric ceramics thus produced, Qmaxwas measured under the following condition and a result thereof wasshown in Table 13 below.

Measurement Condition of Qmax

By the use of an impedance analyzer HP4194A produced by Hewlett-PackardDevelopment Company, L.P., the impedance characteristic was measured ina three-order harmonic mode of thickness longitudinal vibration (60 MHz)to derive Qmax. Qmax contributes to low-voltage oscillation as aresonator and Qmax at 60 MHz is required to be 6 or more. TABLE 13Piezoelectric Pr Content Ceramics (wt %) Qmax (60 MHz) *Sample 11-1 05.9 Sample 11-2 0.02 6.5 Sample 11-3 0.05 6.7 Sample 11-4 0.10 6.5Sample 11-5 0.12 6.1 *Sample 11-6 0.14 5.4Sample with * mark deviates from the present invention.

As shown in Table 13, it was confirmed that the piezoelectric ceramics(Sample 13-2 to Sample 13-5) containing (Ca_(0.97)La_(0.03))Bi₄Ti₄O₁₅being the main component, and Mn oxide and Pr oxide as the secondarycomponents, and further, containing the Pr oxide in a range of 0.02 to0.12 wt % in terms of Pr₂O₃, all had Qmax of 6 or more. Further, Curiepoints of these piezoelectric ceramics were measured like in Example 1and consequently were all 750° C. or higher.

EXAMPLE 14

First, respective powder raw materials of CaCO₃, La₂O₃, Bi₂O₃, TiO₂,MnCO₃, and Ho₂O₃ were prepared as starting substances and weighed sothat a final composition of a main component should be(Ca_(0.97)La_(0.03))Bi₄Ti₄O₁₅ and the content of MnCO₃ being a secondarycomponent should be 0.18 wt % in terms of MnO, and were then subjectedto ball mill mixing (about 16 hours) in pure water by the use ofzirconia balls.

Thereafter, like in Example 1, the obtained mixture was used to obtainpiezoelectric ceramics (Sample 14-1 to Sample 14-6) each having a lengthof 2 mm, a width of 1.25 mm, and a thickness of 435 μm. However, Ho₂O₃was weighed and added to calcined things so that the contents thereofshould be as shown in Table 14 below. On both surfaces of each of thepiezoelectric ceramics, Ag electrodes (diameter 1.5 mm, thickness 1 μm)for evaluating thickness longitudinal vibration were formed by thevacuum deposition method.

With respect to each of the piezoelectric ceramics thus produced, Qmaxwas measured under the same condition as in Example 13, and a resultthereof was shown in Table 14 below. TABLE 14 Piezoelectric Ho ContentCeramics (wt %) Qmax (60 MHz) *Sample 12-1 0 5.9 Sample 12-2 0.02 6.3Sample 12-3 0.05 6.6 Sample 12-4 0.10 6.3 Sample 12-5 0.12 6.1 *Sample12-6 0.14 4.9Sample with * mark deviates from the present invention.

As shown in Table 14, it was confirmed that the piezoelectric ceramics(Sample 14-2 to Sample 14-5) containing (Ca_(0.97)La_(0.03))Bi₄Ti₄O₁₅being the main component, and Mn oxide and Ho oxide as the secondarycomponents, and further, containing the Ho oxide in a range of 0.02 to0.12 wt % in terms of Ho₂O₃, all had Qmax of 6 or more. Further, Curiepoints of these piezoelectric ceramics were measured like in Example 1and consequently were all 750° C. or higher.

COMPARATIVE EXAMPLE 4

Piezoelectric ceramics (Comparative Sample 4) was obtained like in theforegoing Comparative Example 3. On both surfaces of this piezoelectricceramics, Ag electrodes (diameter 1.5 mm, thickness 1 μm) for evaluatingthickness longitudinal vibration were formed by the vacuum depositionmethod.

With respect to the piezoelectric ceramics thus produced, Qmax wasmeasured under the same condition as in Example 13. As a result, Qmaxwas 2.0 and did not satisfy the required characteristic of the resonatorat 60 MHz.

COMPARATIVE EXAMPLE 5

First, respective powder raw materials of SrCO₃, CaCO₃, Bi₂O₃, TiO₂,La₂O₃, and MnCO₃ were prepared as starting substances and weighed sothat a final composition of a main component should be(Sr_(0.33)Ca_(0.67))_(0.9)La_(0.1)Bi₄Ti₄O₁₅ and the content of MnCO₃being a secondary component should be 0.18 wt % in terms of MnO, andwere then subjected to ball mill mixing (about 16 hours) in pure waterby the use of zirconia balls.

Thereafter, the obtained mixture was used to obtain piezoelectricceramics (Comparative Sample 5) like in Example 1. On both surfaces ofthis piezoelectric ceramics, Ag electrodes (diameter 1.5 mm, thickness 1μm) for evaluating thickness longitudinal vibration were formed by thevacuum deposition method.

With respect to the piezoelectric ceramics thus produced, Qmax wasmeasured under the same condition as in Example 13. As a result, Qmaxwas 5.7 and did not satisfy the required characteristic of the resonatorat 60 MHz.

INDUSTRIAL APPLICABILITY

Applicable to electronic devices such as resonators and filters and toproducts and the like such as sensors and actuators that use electriccharge and displacement.

1. Piezoelectric ceramics characterized by containing, as a maincomponent, a bismuth layer-structured compound having (M^(II)_(1-x)Ln_(x))Bi₄Ti₄O₁₅ crystals (M^(II) is an element selected from Sr,Ba, and Ca, Ln is an element selected from lanthanoids, and x is withina range of 0<x≦0.5) and further containing, as secondary components, atleast one of Mn oxide and Co oxide, and lanthanoid, wherein the contentof the lanthanoid being the secondary component falls within a range of0.02 to 0.12 wt % in terms of oxide thereof.
 2. Piezoelectric ceramicsaccording to claim 1, wherein the content of said Mn oxide or Co oxidefalls within a range of 0.02 to 0.62 wt % in terms of MnO or CoO. 3.Piezoelectric ceramics according to claim 1, wherein lanthanoid selectedas Ln is any one of La, Pr, Sm, Gd, Dy, and Ho.
 4. Piezoelectricceramics according to claim 1, wherein the lanthanoid being thesecondary component is any one of Pr, Nd, Sm, Gd, Dy, and Ho.